Method and devices for jointing cables

ABSTRACT

Electrical cables are joined end-to-end within an elongate, imperforate, expandable jointing body. A tubular-shaped mounting tool is inserted into an end of the jointing body and supports at its forward end a separable, forwardly tapered extension cone whose maximum outer diameter substantially corresponds to the desired expanded inner diameter of the jointing body. The mounting tool is inserted into the jointing body when the mounting tool is inserted into the jointing body. A handle rearwardly of the cone permits its removal from the jointing body but the jointing body itself maintains its position so as to maintain an expanded opening in the end of the jointing body. Thereafter, removal of the mounting tool seals the cable joint as a result of contraction of the cross-section area of the jointing body.

TECHNICAL FIELD

The present invention relates to a method and associated devices forjointing a power cable for medium voltage, that is, preferably a powercable intended for use in the voltage interval from 12 kV to 36 kV.

BACKGROUND OF THE INVENTION

When jointing a cable, the conductors of two cable ends are joinedtogether by means of a connector, the respective cores having first beenfreed from the surrounding insulation. The joint with the exposedconnector must then be insulated. This insulation is usually carried outby means of a prefabricated jointing body of rubber. Known jointingbodies are usually designed with substantially cylindrical shells. Thejointing body itself is provided with a continuous cylindrical hole,wherein the hole in a natural, non-elongated state, has an insidediameter somewhat smaller than the outside diameter of the insulation onthe cable which is to be joined. This is necessary for the elasticjointing body, after the jointing operation, to embrace the insulationof the cable ends in order to obtain a tightly fitting joint.

When a jointing operation is to be carried out, the work is initiated bymoving the jointing body to a position of rest over one of the cablecores. The cable ends are prepared, which means exposure of theconductors to be joined and removal of the insulation screens, and theconductors are joined together. The jointing is usually carried out witha ferrule, which by mechanical deformation brings the ferrule intocontact with the conductors. Afterwards, the jointing body is brought toa centered position over the joint. The connector sometimes has a largerdiameter than the cores and can therefore constitute an obstacle topositioning the jointing body right across the joint.

Moving a jointing body over the exterior of a cable without expandingthe jointing body in advance is difficult and means that the jointingbody can only be used on a cable with a well-defined outside diameteradapted to the size of the jointing body. The tolerance range forvariation of outside diameters of cables, for which a certain jointingbody can be used, becomes very limited because a very considerable forceis required to move the jointing body along the cable. Certain knownjointing bodies must be expanded in order for the jointing body to bemoved into position, partly over one of the cable cores prior to thework with jointing of the conductors, partly to be able afterwards tocenter the jointing body over the joint.

It is known to expand the jointing body from the factory on an innercarrier in the form of a thin pipe, which may be built up of a plastictape which is wound into a pipe, the jointing body thus covering theplastic pipe like a cover. The jointing body with its carrier pipe hasthen been given an inside diameter which is larger than both the outsidediameter on the cable to be joined and any connectors in the joint,whereby the jointing body can easily be fitted on the cable according tothe above. After returning the jointing body over the joint, theexpanding plastic pipe is removed by making the end or ends of theplastic tape, from which the pipe is formed, accessible and withdrawablefrom the interior of the jointing body, the jointing body thuscollapsing and surrounding the joint. The disadvantage of thisarrangement is that the jointing body will be expanded for a long timeand then there is a risk that the rubber settles and possibly loses itsre-sealing power, or that the storage time of the jointing body becomeslimited. A further disadvantage is that the amount of material requiredto manufacture the carrier is considerable.

Another known jointing body is made as a cylindrical tube of rubbersurrounded by a cylindrical shell of shrinking hose, to which the rubbertube is applied, whereby the rubber tube is kept stretched. The jointingbody is applied over the joint, as described above, whereupon the rubberbody surrounds the joint when the shrinking hose is heated, at whichtime the expanding forces of the shrinking hose are eliminated, wherebythe re-sealing forces of the rubber tube around the cable cores and thejoint are released. One of the disadvantages of this type of jointing isthat heat must be supplied to the jointing body and further that therubber component of the jointing body is expanded during the entirestorage time of the jointing body.

The object of the present invention is to provide a jointing body whichdoes not need to be expanded until being used, and to show that this canbe achieved by means of a jointing method which utilizes an inexpensiveand partially reusable mounting tool for expanding the jointing body.

SUMMARY OF THE INVENTION

The invention comprises a jointing body made of an elastic material forjointing two cable ends, wherein the jointing body is characterized inthat its ends are each designed as end portions with a longitudinal holere-sealing around the respective cable on each side of a joint, and thatbetween these end portions there is an elongated, substantiallycylindrical inner space with a cross-section area larger than thecross-section area of the holes of the end portions. Further, theinvention comprises a mounting tool for applying the jointing body tothe joint, wherein the mounting tool comprises a mounting pipe and anextension cone insertable therein, the mounting tool when jointing bymeans of the cone being primarily inserted into one end portion of thejointing body, whereby the end portion of the jointing body is expandedonto the mounting pipe, which has a larger inside diameter than thecable. This allows the jointing body to be easily fitted over the cableafter the extension cone has been withdrawn from the mounting pipe. Thesame procedure is used for the other end portion of the jointing bodywhich is expanded in the same way, allowing the entire jointing body tobe easily fitted over one of the cable cores. After joining theconductors, the jointing body is centered over the joint, whereafter themounting pipes are withdrawn from the respective end portions of thejointing body and removed, which results in the end portions re-sealingaround the respective cable.

The advantage achieved through the invention is that, when the frictionhas been reduced, if necessary with the aid of a suitable lubricant, thejointing body can be expanded in a simple manner, on site, by means ofthe mounting tool. This becomes especially simple in the case, asdescribed, where the jointing body has been enlarged in its inner part,since this inner part of the jointing body need not be expanded.However, it is possible to apply the technique described according tothe invention also to jointing bodies with a completely straightcylindrical center hole by first inserting a mounting pipe into one endof the jointing body, the extension cone then being removed, and theninserting a mounting pipe from the other direction into the opposite endof the jointing body. When inserting the mounting tool into the secondend of the jointing body, the extension cone can then partiallypenetrate into the mounting pipe which is inserted from the first end,the jointing body thus being expanded in its full length.

The reason that the end portions with their re-sealing inner holes havea limited extent in the longitudinal direction of the jointing body isthe desire to minimize the forces which are required to expand the innerholes of the jointing body. This is simplified further by performing theexpansion according to the invention from both ends of the jointingbody.

The mounting pipe which, with the aid of the extension cone, is to bemoved into position and expand an end portion of the jointing body isdesigned as a thin-walled tube, which can be cracked and thrown awayafter use. The tube can, of course, also be made in such a way as toenable it to be disassembled and reused after use.

When the jointing body has been moved into position over the joint, themounting pipe can be withdrawn, as mentioned above. This mounting pipemay be provided with indications of fracture to facilitate cracking.

The cross-section area of the mounting pipe is circular, elliptical, orconsists of a rhomboid with rounded corners.

The transition between mounting pipe and extension cone, when the coneis inserted into the pipe, is made such that a smooth transition isobtained.

The jointing body is made in a few sizes, where each size may cover aplurality of cable areas of cables with a certain system voltage, forexample four different sizes for covering cable areas in the interval50-630 mm². The mounting tool can be provided for each size of thejointing body; however, the same tool can be used also for jointingbodies which have been designed for cables with a different systemvoltage.

One advantage with jointing bodies according to the structure describedis that the jointing bodies are characterized by a low weight. Anotheradvantage of jointing according to the method described is that thejointing body described only has to be expanded for the period of timerequired to carry out the jointing operation.

Still another advantage of the jointing according to the invention isthat two separate mounting pipes are used for expanding the jointingbody. One mounting pipe is introduced into each end of the jointingbody. This reduces the force necessary when introducing the pipe intothe body and further the force necessary for withdrawing a pipe from thejointing body compared with the forces needed when using one mountingpipe extending along the whole length of the jointing body.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a longitudinal section through a jointing body with anenlarged inner central portion and two sealing end portions according tothe invention present.

FIG. 2 illustrates the mounting tool with the mounting pipe and theextension cone.

FIG. 3 shows how the insertion of the extension cone into the mountingpipe forms the complete mounting tool.

FIG. 4 illustrates the expansion of one of the end portions of thejointing body by means of the mounting tool.

FIG. 5 shows the removal of the extension cone from the mounting pipe.

FIG. 6 illustrates the withdrawal of the mounting pipe from one endportion of the jointing body, this end portion then being re-sealedaround the cable core.

FIG. 7 shows in a side view the removal of the mounting pipes away fromthe jointing body, a complete joint thus being formed.

FIG. 8 illustrates the removal of the mounting pipe from the cable.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The method and the associated devices according to the invention will bedescribed in the following with reference to the accompanying drawings.

The jointing body 1 is shown in FIG. 1 in a longitudinal section. Aswill be clear from the figure, the exterior of the jointing bodyaccording to the example assumes an almost cylindrical shape withconical transitions to cylindrical terminations at each end. The endportions 2 are illustrated as those portions of the jointing body 1which have a cylindrical hole 3 with a cross-section area which isadapted to be somewhat smaller than the outer area of a prepared cable,around which the end portion is to re-seal tightly when the joint iscompleted. Between the two end portions 2 there is a central portionwith an inner space 4, the inner space having a substantially elongatedcylindrical shape. The cross-section area of this inner space 4 islarger than the cross-section area of the cylindrical holes 3 of the endportions. The cross-section area of the inner space 4 should be at leastso large that the walls of the inner space 4 need not be expanded whenthe jointing body 1 is to be fitted over a cable core or be centeredover a joint.

The jointing body 1 is suitably made of rubber, but other elasticmaterials can be utilized as well. The external layer of the jointingbody as well as the internal surfaces of the substantially innercylindrical space 4 consist of a flexible conducting layer to controlthe electric field at the joint in a known manner. The inner wall(envelope surface) of the inner space 4 can be made with a thin,conducting, elastic transverse wall or film, preferably arranged with ahole for the cable at the center, the task of this wall or film being toprovide a conducting connection between the connector and the conductinginner layer of the inner space 4. As an alternative to a transversewall, elastic conducting flaps or tongues can be used. Otheralternatives include resilient wires or tongues. Common to theseconducting means is that they may not constitute any obstacle to theinsertion of a prepared cable into the jointing body.

The complete mounting tool to manufacture a joint with the aid of thejointing body 1 is shown in FIG. 2. The mounting tool 5 is, inprinciple, composed of two parts, namely, an extension cone (extensionmeans) 6 with an associated handle 7 on a shaft 7a and the mounting pipe8. FIG. 2 shows the extension cone 6 fully inserted into the mountingpipe 8.

According to the example shown, the extension cone 6 has the shape of atruncated cone and can thus have a square termination at the front endand has a diameter at its tip of such a magnitude as to allow it to beintroduced into the cylindrical hole 3 at the end portion 2 of thejointing body 1. Other geometries of the extension means 6 with anexpanding function according to the invention can, of course, also beused. When the mounting tool 5 is inserted into the end portion 2, thetask of the extension cone 6 is to expand the hole 3 of the end portionto such an extent that the mounting tool 8 can be inserted fully intothe end portion 2. At its widest part, the extension cone 6 forms aneven, smooth transition towards the mounting pipe 8 due to the fact thatthe mounting pipe 8 is bevelled at the transition. The mounting pipe 8is formed from a cylindrical tube with a thin shell, one end of whichterminates in a flange 8a.

As shown in FIG. 3, the shaft 7a of the extension cone 6 is providedwith a support 7b which, when joining the extension cone 6 and themounting pipe 8 into a mounting tool 5, upon contact with the flange 8aof the mounting pipe, places the mounting pipe 8 in the correct positionin relation to the extension cone 6, such that the described transitionbetween the pipe and the cone is smooth.

In the jointing process, the extension cone 6 is inserted into themounting pipe 8, whereupon the complete mounting tool 5, lubricated, isinserted into the end portion 2 for jointing body (see FIGS. 4 and 5).This causes this end portion 2 to be expanded onto the mounting pipe 8such that the area of the cylindrical hole 3 of the end portion 2 isequal to the outer area of the mounting pipe 8. By gripping around thehandle 7, the extension cone 6 can now be withdrawn and removed from themounting pipe 8 (FIG. 5) which remains in the end portion 2 and keepsthis portion expanded. The same procedure is used for the other endportion 2 of the jointing body 1, such that this end portion alsobecomes expanded onto another mounting pipe 3. Thus, when both endportions 2 are expanded, the jointing body 1 can be fitted over one ofthe cable cores 10. The actual jointing of the conductors of the cableis carried out in a known manner, for example with the aid of aconnector or by means of other methods.

When both cables 10 and 11 are joined, the jointing body 1 is returnedby moving it along the cable and centering it over the joint. Since thejointing body 1 is kept expanded by the mounting pipe 8, this causes noproblems since the inside diameter of the mounting pipes 8 is largerthan the diameter of the connector. In addition, the enlarged innerspace 4 provides space for the connector.

When the jointing body 1 is centered over the joint, the mounting pipe 8is withdrawn from the jointing body 1 (see FIGS. 6 and 7), whereby theend portions 2 recover their original shape and tightly surround the twocables 10 and 11 on both sides of the joint. The withdrawal from themounting pipes 8 is facilitated by providing these with wings 12 at aflange 8a on the mounting pipe 8 which remains outside the jointingbody 1. The wings 12 are utilized as handles when withdrawing themounting pipe 8 from the end portion 2.

When the mounting pipes 8 are withdrawn, they are removed from the cableby splitting them at a notch 14, the pipes 8 then being broken apartwith the aid of the wings 12 and being removed from the cable. The jointwith the jointing body is then covered in a known manner in order toprotect the joint from mechanical or other damage.

The mounting pipe 8 can be provided with longitudinal indications offracture or be dividable, allowing the mounting pipe to be removed fromthe cable and be reused. In the simplest case, the mounting pipe 8 is inthe form of a stiff and thin plastic material, the mounting pipe 8 thusforming a disposable article.

The mounting pipes 8 and the described process can be utilized also withjointing bodies which have a continuous cylindrical hole, which is to beextended in its entirety. The disadvantage of this is that considerablygreater forces must be used to extend the inner hole of the jointingbody.

The mounting pipe 8 is intentionally described as cylindrical in orderthus to comprise all types of cylinders, in which a section through theenvelope surface of the cylinder shows a closed curve. The mounting pipe8 can thus possess shapes which are adapted to cables with differentgeometries of their cross-sectional area.

What is claimed is:
 1. A method for insulating a joint between twocables, comprising the steps of:forming a tubular jointing body havingtwo ends each having an elastically expandable end portion with an innercircumference smaller than the outer periphery of the cables to bejointed; inserting a separate mounting tool into each of said endportions whereby said end portions are expanded onto an outer surface ofsaid mounting tool and wherein a passageway is formed through saidjointing body and said mounting tools, said passageway having an innerdimension greater than the outer periphery of the cables to be jointed;slipping said jointing body, with said mounting tools inserted in eachend portion, onto one of the cables to be jointed; jointing said cablestogether; centering said jointing body over the joint; and removing fromeach of said end portions said mounting tool, whereby said end portionscontract by reason of their elasticity, so as to be securely fittedabout the cables.
 2. A method for jointing two power cables according toclaim 1, wherein said mounting tool comprises a mounting pipe and anextension cone and wherein said step of inserting further comprises thesteps of:expanding each of said end portions radially by inserting saidextension cone therein; sliding said end portions onto the outside ofsaid mounting pipe as said extension cone is inserted into said endportions, whereby said end portions are expanded onto an outer surfaceof said mounting pipe; and completely removing said extension cone fromsaid mounting pipe and said jointing body whereby said passageway havingan inner dimension greater than the outer periphery of the cables to bejointed is formed through said jointing body and said mounting pipe. 3.A method for jointing two power cables according to claim 2, whereinsaid removing of said extension cone is achieved by pulling saidextension cone rearwardly out of said mounting pipe.
 4. A method forjointing two power cables according to claim 2, further comprising thestep of lubricating said mounting tool prior to insertion into each ofsaid end portions.
 5. A method for jointing two power cables accordingto claim 1, wherein said step of removing said mounting pipe from eachof said end portions is achieved by pulling said mounting piperearwardly out of said end portion and thereafter splitting saidmounting pipe and removing it from the jointed cabled.